The compound cyclosporine (cyclosporin A) has found wide use since its introduction in the fields of organ transplantation and immunomodulation, and has brought about a significant increase in the success rate for transplantation procedures. Unsatisfactory side-effects associated with cyclosporine, however, such as nephrotoxicity, have led to a continued search for immunosuppressant compounds having improved efficacy and safety.
Recently, several classes of macrocyclic compounds having potent immunomodulatory activity have been discovered. Okuhara et al., in European Patent Application No. 184,162, published Jun. 11, 1986, disclose a number of macrocyclic compounds isolated from the genus Streptomyces. Immunosuppressant FK-506, isolated from a strain of S. tsukubaensis, is a 23-membered macrocyclic lactone represented by formula 1a, below. Other related natural products, such as FR-900520 (1b) and FR-900523 (1c), which differ from FK-506 in their alkyl substituent at C-21, have been isolated from S. hygroscopicus yakushimnaensis. Yet another analog, FR-900525, produced by S. tsukubaensis, differs from FK-506 in the replacement of a pipecolic acid moiety with a proline group.
FR-900520, also known as ascomycin, has been previously disclosed by Arai et al. in U.S. Pat. No. 3,244,592, issued Apr. 5, 1966, where the compound is described as an antifungal agent. Monaghan, R. L., et al., on the other hand, describe the use of ascomycin as an immunosuppressant in European Patent Application No. 323,865, published Jul. 12, 1989.
Although the immunosuppressive activity of FK-506 has been clinically confirmed, toxicity in mammals has limited its utility. The activity of FK-506 has, however, prompted efforts to discover novel analogs of FK-type compounds which possess superior properties. These efforts include the isolation of new fermentation products, the microbial transformation of existing chemical entities, the chemical modification of these macrocycles, and the synthesis of hybrid species derived from smaller synthetic fragments. ##STR3##
Fermentation products of FK-type compounds include C-21-epi derivatives of FK-506; a 31-demethylated derivative of FK-506; 31-oxo-FK-506; and compounds derived from FK-506, FR-900523 and FR-900525 which are characterized by the introduction of hydroxy-protecting groups, formation of a double bond by elimination of water between carbons 23 and 24, oxidation of the hydroxy group at carbon 24 to the ketone, and reduction of the allyl side-chain at carbon 21 via hydrogenation. Other published derivatives include those derived from FK-506 and FR-900520 where the lactone ring is contracted to give a macrocyclic ring containing two fewer carbons.
Several microbial transformations of FK-type compounds at carbon 13 have been published, such as the microbial demethylation of FR-900520 to form the bis-demethylated 13,31-dihydroxy ring-rearranged derivative of FR-900520; the microbial monodemethylation of FK-506 and FR-900520, respectively; and the microbial demethylation of FR-900520 at C-31, as well as a number of other macrocyclic microbial transformation products.
Numerous chemical modifications of the FK-type compounds have been attempted. These include the preparation of small synthetic fragments of FK-type derivatives; a thermal rearrangement of a variety of derivatives of FK-506 which expands the macrocyclic ring by two carbons; and modifications which include methyl ether formation at C-32 and/or C-24, oxidation of the C-32 alcohol to the ketone, and epoxide formation at C-9.
Although some of these modified compounds exhibit immunosuppressive activity, the need remains for macrocyclic immunosuppressants which do not have the serious side effects frequently associated with immunosuppressant therapy. Accordingly, one object of the invention is to provide novel semisynthetic macrolides which possess the desired immunomodulatory activity but which may be found to minimize untoward side effects.
Another object of the present invention is to provide synthetic processes for the preparation of such compounds from starting materials obtained by fermentation, as well as chemical intermediates useful in such synthetic processes.
A further object of the invention is to provide pharmaceutical compositions containing, as an active ingredient, at least one of the above compounds. Yet another object of the invention is to provide a method of treating a variety of immune system-related disease states, including post-transplant tissue rejection and autoimmune disfunction.